This invention relates generally to a switch circuit that enables reliable long-term operation over a wide range of input voltages. More particularly, the invention relates to a switch architecture that enables reliable, long-term, on/off switch operation over a range of voltages.
The use of small geometry and low-voltage devices (i.e., devices that reliably operate when the voltage across any two transistor terminals is less than a relatively low maximum voltage) is the trend in advanced integrated circuits (ICs). These low-voltage digital-logic devices consume less power and can be reliably operated at higher clock rates. Accordingly, low-voltage devices are used in a number of battery-operated portable electronic systems. Intermediate voltage-level devices (i.e., devices that reliably operate when the voltage across any two transistor terminals is less than approximately 3V) are generally used in ICs that require analog functions. Even higher voltage levels are required by some circuits used in both analog and digital functional blocks related to system interfaces and other functions. One way to accommodate these higher voltages is to use transistors designed to reliably operate at corresponding voltage levels. For example, transistors where the voltage across any two transistor device terminals can be 5V without reliability issues (i.e., 5V transistors) can be used to manage inter-IC power (e.g., on/off) functions over a range of voltages from 0V to about 5V. This solution requires a second IC or the addition of devices designed to manage these higher voltages when the bulk of IC functionality is provided via a first IC that uses lower-voltage devices. Accordingly, ICs using higher-voltage transistors in addition to low-voltage devices result in increased cost and complexity for the final product.
Typically, IC manufacturers do not provide a product that combines low-voltage digital transistors, 3V analog input/output transistors and 5V analog/power transistors using a single manufacturing process. Accordingly, there would be a significant cost associated with using and developing a semiconductor wafer manufacturing process that could provide the desired combination of transistors on a single IC.
Other known solutions for power management have a limited operational voltage range. These solutions suffer from poor reliability when devices are required to handle voltage levels that are higher than the upper limit of their operational voltage and from bias-circuit leakage and low input impedance when voltage levels are lower than the lower limit of their operational voltage range. Although a limited operational voltage range is not a concern for some applications, some other applications require better switch properties, such as lower current leakage and higher input impedance at low voltage levels and increased reliability at high voltage levels. For example, the universal serial bus on-the-go (USB-OTG) extension of the USB 2.0 specification includes a session-request protocol (SRP) that requires extremely good switch “off” properties for power bus voltages from 0V to 2V and requires the power bus voltage to go as high as 5.25V.
Therefore, it would be desirable to provide a low cost, reliable and integrated power management solution that can be implemented using existing semiconductor manufacturing process technologies.